Dolomites and salinity: a comparative geochemical study

A geochemical study of ancient (Permian to Neogene) dolomites that were formed under widely different salinities revealed certain distinct characteristics: 1) marine (non-evaporitic) dolomites vary in their calcium content from stoichiometric to calcian (57 mole percent, and their sodium content is 150-350 ppm; 2) dolomites in association with gypsum cover the same range of stoichiometry as the marine dolomites, but their sodium content reaches much higher values (as high as approximately 2700 ppm). Furthermore, a negative correlation is present between excess calcium and sodium; and 3) dolomites in association with halite have an almost ideal stoichiometric composition and a sodium content overlapping the lower range of marine dolomites (150-270 ppm). -from Authors